The concentration of Aspergillus candidus in samples of grain dust and of air polluted with grain dust was found to be large (respectively 3.0 x 10(5) - 3.0 x 10(9) cfu/g and 5.0 x 10(3) - 6.47 x 10(5) cfu/m(3)) and proved to be significantly greater compared to samples of other organic dusts (p<0.001). Rabbits exposed to long-term inhalation of the cell extract of A. candidus revealed a positive cellular and humoral response, demonstrated by the significant (p<0.01) inhibition of leukocyte migration in the presence of specific antigen and by production of precipitins against antigen of the fungus. The inhibition of leukocyte migration was even stronger in another group of rabbits exposed twice to the inhalation of live A. candidus spores. A group of grain workers reacted significantly more frequently to extract of A. candidus in the leukocyte migration inhibition test (p<0.01) and precipitation test (p<0.05), compared to the control group not exposed to organic dusts. It was concluded that Aspergillus candidus, because of its common occurrence and strong immunomodulating properties, poses an important occupational hazard for grain handling workers. First, Rice husk, millet straw, guinea corn stalk and sawdust were used as fermentation feed substrate for the evaluation of cellulase activity secreted by Aspergillus candidus. The substrates were pretreated with 5% NaOH (alkaline treatment) and autoclaved . From the fermentation studies, rice husk, millet straw and guinea corn stalk feed substrates showed the highest cellulase activity of 7.50, 6.88 and 5.84 IU, respectively. The effect of pH showed that optimal pH for maximum cellulase activity varied in each of the substrates used. Rice husk and millet straw had maximum enzyme activity at pH 5, while guinea corn stalk and sawdust had maximum activity at pH 3 and 4, respectively. From this study, Aspergillus candidus holds the potential of converting lignocellulose materials into products of commercial and industrial values such as glucose and other biofuels.
==> DISCUSSIONCellulase activity of Aspergillus candidus, using rice husk, millet straw, guinea corn stalk and sawdust as cellulosic substrates showed the highest enzyme activity was on the 7th day (168 h) for rice, millet and sawdust media and on 8th day (192 h) for the guinea corn stalk medium after 240 h fermentation period. At 168 h period, rice husk medium had the highest cellulase activity of 7.50 IU; while millet and guinea corn substrates had activities of 6.88 and 5.84 IU. However, sawdust feed substrate had a significantly low cellulase activity of 4.79I U. The differences in the cellulase activity observed in the different culture media could be attributed to the differences in the chemical composition and concentration of other macromolecules such as lignin and hemicellulose that exists in natural association with cellulose. The sawdust used was obtained from hardwood, had higher lignin content when compared to the other feed substrates which belong to the Cereal family. Lignin which forms a physical seal around cellulose inhibits cellulase from hydrolyzing the cellulose and hence this may affect the cellulase secreted by the organism as can be observed with sawdust substrate. This observation is in relation with the findings of Ojumu et al. (2003), who reported a low cellulase activity. Again, alkali pretreatment of sawdust cellulosic material may not be an efficient method of accessing cellulose by cellulase enzyme as reported by Gharpuray et al. (1983). The differences observed in the cellulase activity could also be attributed to the facts that, although the residues are distinctive in outward appearance, these materials all comprise of about 40-50% cellulose, 20-30% hemicellulose with lesser amounts of lignin in cereals and herbaceous plants but higher in forestry residues (sawdust) (Wyman, 2008). More efficient technologies like steam explosion pretreatment must be applied to completely degrade lignin and gain access to the cellulose molecules. Although, these substrates were pretreated to delignify them, only a significant percentage of the total lignin content was removed. The organism through cascades of enzymatic actions must therefore degrade the remaining to enable its unlimited access to the cellulose molecule. As reported by Kirk et al. (1980), combination of biological and chemical agents enables the complete degradation of lignin. Organic acids such as oxalate produced by the organism inhibit lignin peroxidase, a lignin degrading enzyme and this could also be responsible for the differences in the cellulase activity (Kirk et al., 1980).Another factor that may lead to the differences in cellulase activity is the production of non-specific by-products other than glucose by unspecified side reactions. These by-products promote glucose degradation and reduce its yield. Pretreatment of sawdust for example enhances the production of proteins which leads to a corresponding increase in ethanol production from glucose as reported by Ryu and Lee (1983). The submerged fermentation culture method used in this study may also contribute to the differences in cellulase activity. A comparison of solid state fermentation and submerged fermentation has shown that submerged method has shearing forces which rupture mycelial cells and deactivate enzymes, thus enzyme activity is decreased (Wase et al., 1985). The decrease in cellulase activity shown by the fungus after attaining its maximum peak period of enzyme secretion could be attributed to so many other factors. Products of cellulase action on cellulose (cellobiose and glucose) inhibit enzyme secretion. Depletion of carbon and nitrogen sources causes starvation and hence the fungus may not grow and cellulase activity is growth related as reported by Dosoretz et al. (1990). The effect of pH on cellulase secretion shows that each substrate supports a particular pH for maximum enzyme secretion. Beldman et al. (1985) reported that Aspergillus species grow and metabolize well in acidic pH medium between pH 3-5. Linder and Teeri (1996) also proposed that cellulases produced by filamentous fungi rely on several aromatic amino acids for high binding capacity to cellulose surface and this might enhance enzyme activity.

Outdoor Location
Found in warm soils, grain, and secondary decay of vegetationPotential Toxin Production
Can produce petulin which may be associated with disease in humans and other animalSpore Size
Conidia dimensions 3-4.5 x 2.5-4.5 microns

Outdoor Location
Found in warm soils, grain, and secondary decay of vegetationPotential Toxin Production
Can produce petulin which may be associated with disease in humans and other animalSpore Size
Conidia dimensions 3-4.5 x 2.5-4.5 microns